The invention discloses polybasic fluxing agents used for analyzing carbon and sulphur content in a metal or nonmetal sample and a preparation method thereof. One polybasic fluxing agent comprises the following components in parts by weight: 1.5-2 parts of tungsten, 0.3-1 part of iron, 0.1-0.3 part of tin and 0.1-0.5 part of vanadium pentoxide; and another polybasic fluxing agent comprises the following components in parts by weight: 1.5-2 parts of tungsten, 0.3-1 part of iron and 0.1-1 part of copper. A powder metallurgy porous material matrix consists of tungsten and iron, and tin or copperis molten and permeates into the pores of the powder metallurgy porous material matrix. The polybasic fluxing agents have good uniformity and meltbility and can be added in one step with small addition error, and dust generated during combustion is relatively less; therefore, the accuracy of carbon and sulphur analysis can be improved greatly.